This application claims the priority of European Patent application 99 121 549.2, filed Oct. 29, 1999, the disclosure of which is incorporated herein by reference in its entirety.
The present invention concerns a stabilized accelerator of low viscosity for the setting and hardening of a hydraulic binder, its use and a method for setting hydraulic binders using said accelerator.
Many substances that accelerate the setting and hardening of concrete are already known. The most usual are i.e. strongly alkaline reacting substances such as alkali hydroxides, alkali carbonates, alkali silicates, alkali aluminates and alkaline earth chlorides. With strongly alkaline reacting substances undesired annoyance of the user occurs. Such products may cauterize the skin and cause inflammation of the eye or they may cauterize the cornea thereby affecting the strength of vision. Due to inhalation of the dust or aerosol generated during use, furthermore detrimental effects on the respiratory system may develop.
In view of concrete technology, very alkaline setting accelerators reduce the final strength and enhance the shrinkage, what may cause crack formation and therefore may reduce the long lasting properties, in particular the resistance to sulfates of such concrete.
Besides of the above-mentioned strongly alkaline accelerators also already other accelerators have been described.
Accelerators for the setting of hydraulic binders on the basis of amorphous aluminum hydroxide are already known from EP-A 0 026 262, in particular claims 1 and 11 to 13, as well as from Chemical Abstracts Vol. 86, No. 18, May 1977, page 300, 126087c.
According to EP-A 0 026 262, page 2, last paragraph, the particle size of the amorphous aluminum hydroxide is in particular in the range between 4.8 and 5.4 xcexcm.
In such hardening accelerators also cellulose products that are able the swell and further admixtures may be present, see EP-A 0 026 262, in particular claims 8 to 10 and the examples.
From DE-A 2 548 687, in particular claim and page 15, the addition of aluminum sulfate or nitrates to setting accelerators on the basis of aluminates and aluminum oxide is known.
From FR-A 2 471 955, in particular claims 1 to 6, the use of formiates and nitrates in accelerators is known.
EP 0 076 927 describes a method for accelerating the setting by addition of amorphous aluminum hydroxide and at least one water-soluble sulfate and/or nitrate and/or formiate.
EP 181 739 A1 describes the use of calcium sulfo-aluminate and a mixture of calcium aluminates that together with alkalis or earth alkalis upon addition of 250% water result in a hardenable slurry.
JP 63 206 341 A2 protects an accelerator of calcinated alunit, calcium sulfoaluminate, sodium aluminate, sodium carbonate.
JP 58 190 849 A2 describes a mixture of calcium sulfoaluminate, calcium sulfate hemihydrate and calcium hydroxide for the preparation of fast setting, sprayable coatings.
SU 697 427 mentions a fast setting concrete due to admixture of calcium aluminate, calcium sulfoaluminate, calcium oxide, ferrite, silicate and gypsum.
JP 54 027 817 mentions the accelerated hardening of gypsum by addition of calcium sulfoaluminate.
JP 53 099 228 describes an accelerator for casting mortar based on calcium sulfoaluminate and calcium fluoroaluminate and water reducing agents.
In DE-OS 2 163 604 accelerators based on calcium fluoroaluminate are mentioned.
From JP 01 290 543 A2 mixtures of calcium sulfo-aluminate and calcium sulfate and lithium carbonate are known as accelerator for low temperature application.
SU 1 350 135 A1 discloses fast setting clinker due to supplementation with barium sulfate, calcium aluminate and calcium sulfoaluminate.
WO 97/36839 discloses the use of lithium silicate and/or lithium aluminate and/or aluminum salts.
WO 98/18740 comprises a method for the production of a setting and hardening accelerator for hydraulic binders. The product that according to claim 1 necessarily consists of 5 components is very turbid, has a high viscosity and a low storage stability. Said accelerator may lead to the plug up of the spray nozzle. At the construction site, the high viscosity results in problems during the dosing of the product, in particular at low temperatures. A dilution of the product is not possible since thereby a part of the basic salts are precipitated. The low pH-value results in corrosion at the dosing and spraying devices.
The goal of the present invention was to provide a composition that acts as setting and hardening accelerator and that preferably is alkali-free and chloride-free and by which very fast setting can be achieved.
Hence, it is general object of the invention to provide a stabilized composition of low viscosity suitable to act as accelerator for the setting and hardening of a binder or a binder comprising mixture, said accelerator comprising at least one aluminum salt, at least one complexing agent for the aluminum and at least one corrosion inhibitor.
A further object of the present invention is a method wherein 0.1 to 10% by weight referred to the weight of the binder of the composition according to the invention is added to said binder or binder comprising mixture.
Possibilities for the application of the composition according to the invention and the method according to the invention is in the production of pre-casting elements and the acceleration of concrete produced at the construction cite. In the first case, the heating (by means of electro heating, or oil heating, or steam), usually applied for accelerating the hardening, can be reduced or even eliminated. In the second case the demolding times of the concrete may be shortened, or the further application of concrete may be continued also at low temperatures. Further applications are in the production of fast setting cement mixtures and mortar mixtures, in particular for fixing prefabricated units, castings etc.
A specific field of use is in particular spraying mortar and spraying concrete. Such mortar and concrete serve the production of buildings of underground and surface engineering as well as the completion and lining of underground, natural or technically produced cavities, such as pit constructions, tunnel constructions or mining constructions, for which the concrete must meet the static requirements as well as being water impermeable. They also serve the consolidation of trenches, slopes, loose walls of rock etc.